1. Field of the Invention
The present application relates to a laser apparatus and a method to re-tune an emission wavelength of a wavelength tunable LD.
2. Prior Arts
One type of a wavelength tunable semiconductor laser diode (t-LD) has been practically used where the emission wavelength of the t-LD may be tuned by thermally varying the refractive index of semiconductor materials by heaters (for example, see Japanese Patent Application Publication No. 2013-33892). A combination of a chirped sampled grating distributed Bragg reflector (CSG-DBR) and a sampled grating distributed feedback (SG-DFB), where the former device inherently shows a plurality of reflection peaks, while, the latter device shows a plurality of gain peaks, may bring about the Vernier effect between the reflection peaks and the gain peaks. The emission wavelength becomes a wavelength at which one of the reflection peaks coincides with one of the gain peaks. The reflection peaks and the gain peaks may be thermally modified by heat generated by the heaters.
In one application of the t-LD, the re-tune of the emission wavelength has been requested to be done quickly. However, the thermal process inherently shows a longer response from the application of heat to the variation of the refractive index of the semiconductor material. Accordingly, such a t-LD accompanied with heaters to tune the emission wavelength shows a longer period to make the re-tuned emission wavelength in stable.